The overall goal of this study is to use the sister chromatid exchange (SCE) assay as a complement (or possibly alternative) to the human stem cell assay for predicting the response of human brain tumor cells to subsequent chemotherapy. We believe the SCE assay will be a more sensitive and rapid assay than the colony forming efficiency (CFE) assay; also the SCE assay should provide important information about the heterogeneity in drug response of the human tumor subpopulations. Specifically, we propose to: 1) determine the optimum conditions for performing the SCE assay in human brain tumor cells; 2) obtain the dose response relationship of human brain tumor cells for each selected drug using the SCE assay; 3) establish criteria for categorizing the relative sensitivity of the tumor cells to selected drugs; categorize the cells as to their relative sensitivity to the drug; and, compare this predicted chemosensitivity both with that obtained using the CFE assay and with the clinical response of the patients; and, 4) investigate the use of the SCE assay to determine human tumor cell heterogeneity with respect to drug response.